Name: Indian Journal of Medical Research Publisher: Indian Council of Medical Research Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Health Copyright: COPYRIGHT 2008 Indian Council of Medical
Research ISSN:0971-5916

Iodine deficiency disorders (IDD) are a major global pubic health
problem. As per the estimates of WHO in 1999, 130 out of the 191 Member
States are affected by IDD. Of the remaining 61 countries, IDD has
either been eliminated or is not known be present in 20 countries. There
are insufficient data from the remaining 41 countries. Most of the
affected regions of the globe, are in Africa (44 countries out of 46)
and South East Asia (9 countries out of 10) (1).

Cause of IDD is deficiency of iodine in the soil. In the regions
where there are repeated flooding and glaciations, the iodine gets
leached out of the upper crust of the earth leading to environmental
iodine deficiency. The vegetation as well as grass grown on such soil
leads to iodine deficiency in food consumed by humans and animals. To
correct this, most of the affected countries have taken different
measures to supply iodine to the population. These include iodized salt,
iodized oil injection, iodized oil capsules (oral), and iodization of
drinking water (1). Some of these are short-term measures but the best
long term method is use of iodized salt, as salt is taken in fixed
amount by everybody, every day round the year and by all age groups.
Thus salt is used as a vehicle for supply of iodine in majority of the
countries (Universal salt iodization programme).

WHO/UNICEF/ICCIDD have jointly recommended outcome and process
indicators to track the progress of IDD elimination (2). Of the several
indicators recommended in developing countries, goitre grading and
urinary iodine levels are the most feasible to use as outcome indicators
while iodine content of salt is the best as a process indicator. The
WHO/UNICEF/ICCIDD recommendations provide separate cut off points for
these indicators to assess the severity of IDD as well as for tracking
IDD elimination programmes. Recent surveys carried out in Bhutan, Nepal,
Thailand as well as seven States in India provide evidence that suggests
that it is essential to view the results of these three indicators in
totality rather than in isolation to make proper assessment of progress
of IDD elimination programme (3).

Chandra et al (4) in this issue have studied 1286 school children
between the age group of 6 to 12 yr in Imphal east, north-east India.
Urine samples (n=160) were analysed amongst the study population, 40
from each locality for Iodine and thiocyanate levels. Goitre rates were
high in spite of adequate iodine intake as judged by iodine content of
salt and urinary iodine excretion pattern in the population studied.
Authors implicate the intake of thiocyanate in proportion to iodine as a
responsible factor for goitres seen. However, the I/SCN ratio was way
above 7 in 95 per cent of the samples analysed only 5 per cent showed
this ratio less than 7 and none below 3, a critical level at which
goitre develops.

WHO, UNICEF, ICCIDD (2) had recommended three criteria for
elimination of IDD, goitre rates less than 5 per cent, median urinary
iodine levels above 100 [micro]g/l, and 90 per cent of households having
adequate iodine intake. Recent studies in 3 countries and 7 States of
India have shown that goitre rates are little on higher side with median
urinary iodine excretion above 100 [micro]g/l but only 50 per cent of
household taking adequate amount of iodine (2). The higher goitre rates
in these studies were attributed to not consuming adequate amount of
iodine by the population, however, in the study by Chandra et al (4)
intake of iodine was satisfactory in more than 90 per cent of house
holds. This naturally brings out the question of what is causing goitre
in this area.

Goitrogenic substances taken in the diet interfere with proper
utilization of available iodine by the thyroid gland. There are two
types of goitrogens described, one type which interferes with iodine
uptake by the thyroid gland and include thiocyanate and perchlorate,
while the other type are substances which inhibits the thyroid organic
binding and coupling i.e., formation of thyroid hormones (5). Both types
of goitrogens will lead to less formation of thyroxine thereby
increasing circulating levels of thyroid stimulating hormone (TSH) which
is responsible for thyroid enlargement i.e., goitre.

The results of the above study (4) do not support implication of
thiocyanate (as shown by I/SCN ratios in urine), while possibility of
other goitrogens which interfere with organification and coupling, needs
further investigation.

Before implicating the role of goitrogenes, it is essential to
undertake further investigations in the population to resolve the public
health problem. The following investigations need to be done: (i)
Circulating levels of T4 and TSH, (ii) [sup.131] I uptake, (iii)
perchlorate discharge test, (iv) plasma inorganic iodide concentration,
and (v) mono iodotyrosine (MIT), di iodotyrosine (DIT) levels in
circulation.

Such investigations should throw more light on possible role of
goitrogens in the population. The findings of Chandra et al (4) have
raised some queries/doubts. Are there factor/factors other than iodine
deficiency which cause goitre in the population? Implication of
goitrogens need further investigations as mentioned above. Other
possibility is genetic defects in the population which also needs a
systematic study amongst the population in Imphal.